Placebo response

What is placebo response?

Placebo effects in pharmaceutical trials vary widely, with response rates varying from 20% to 70%. The placebo response can include improvement in symptoms and even adverse reactions that have been associated with the antipsychotic being tested. Placebo effects can substantially influence conclusions about the efficacy of antipsychotic medications as they reduce any differences in response to the antipsychotic and the placebo.

What is the evidence for placebo response?

Moderate to high quality evidence suggests there is a significant positive placebo response over 12 weeks, which may be most apparent in studies with more efficacious drugs, younger samples, shorter illness duration, shorter study duration, increased number of study sites, and non-university or non-Veteran Affairs settings. Moderate quality evidence suggests improvement in symptoms is greater for patients taking antipsychotics than for patients taking placebo.

Moderate quality evidence suggests there is increased improvement in symptoms from baseline to follow-up in placebo arms of clinical trials over time (1960 to 2014). Conversely, there is decreased improvement in symptoms from baseline to follow-up in treatment arms of clinical trials over time. This may be explained by enrollment of less severely ill patients at baseline in more recent studies, thereby decreasing the treatment effect, and higher expectations in more recent studies that medications will improve symptoms, thereby increasing the placebo effect.

March 2019

Last updated at: 3:33 am, 1st April 2019
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